2001 Toyota Tacoma Oxygen Sensor

Question

How can one determine if the upstream 0-2 sensor is defective. It is the heated one

Answer 1

Defective 02 sensor you can use a scan tool and read its live data a good upstream 02 sensor should  switch from lean to rich,

 Here a vehicle with a faulty 02 sensor, it switching time is ineffective

 Here the replaced 02 sensor it switches lean to rich. and stay within it prescribe hertz.